The present invention is directed to multiple-layer bags which are used to protect materials against contamination from moisture and/or fine particle intrusion.
An example of a multiple-layer bag known in the prior art comprised one or more outer layers, typically fabricated from kraft paper or similar strong but porous paper material. One or more inner layers would also be provided, which would be fabricated from a moisture and fine particle-proof material. The inner and outer layers would be either laid together and rolled into a tube, or separately formed into tubes, with an inner tube then being inserted into the outer tube. In either case, the open ends of the tubes would be flush with one another. In order to prepare the bag for filling, the end of the bag would be flattened. A closure strip would then be folded across the flattened open mouth of the bag, and then sewn shut, often with a "basting" stitch, which would enable rapid opening of the bag by pulling on one particular end of the stitch. A tape or tearstrip might be incorporated into the basting stitch to facilitate removal of the thread. Once the end had been sewn, the sewn end of the bag would be folded over and glued to the side of the bag, with the basting stitch "up", thus producing a bag with one closed end and one open end, ready for shipment to a packager for filling. Once the bag was filled, the packager would then flatten, sew shut, fold and glue the open end of the bag in the same or other conventional manner. While this method produces a relatively strong closure of the bag and is appropriate for materials for which moisture and small particle contamination is not a significant concern, such a closure method does contain the possible drawback that infiltration of moisture and/or migration of fine particles is possible.
Subsequent development in the fabrication of such multiple-layer bags was the introduction of an inner layer fabricated from a moisture and fine particle impervious material, such as polyethylene. Such materials possess the additional characteristic that they can be sealed closed, utilizing heat to form a hermetic seal. The construction of such bags, however, entails more sophisticated and complex manufacturing steps. This prior art bag is formed with the outer layer(s) and the inner layer laid atop one another prior to formation into tubes. The blank formed thereby would then have ends cut in a particular manner so as to produce a stepped configuration of the inner and outer layers on both "sides" of the flat-folded opening. The ends of the bag are then passed through a heat sealing device to close an end of the internal heat-sealable liner. The end of the bag is then folded over and the various exposed sides of the stepped layers affixed to one another with adhesive, thus creating a relatively flat closure of the end of the bag.
The heat-sealed, stepped-end bag, while providing a hermetically sealed inner bag portion, does possess several potential drawbacks. Firstly, opening of the bag is more difficult and more destructive of the overall bag structure, as compared to the sewn-end bag. In addition, the machinery and processes required to create the relatively complex pattern of stepped cuts in the several layers are relatively expensive. In addition, the stepped-end bag construction is capable of providing or producing only a single, given potential bag volume which a packager may use. By contrast, a sewn-end bag enables the customer to selectively shorten the flush cut ends, if he so desires, to package volumes smaller than those which the readymade bag is capable of enclosing.
It is accordingly desirable to provide a bag which is relatively inexpensive to manufacture, and requires relatively less complex machinery and processes to fabricate.
It is a further object of the invention to provide a bag for providing protection against moisture infiltration and fine particle migration, which has an easy-open construction.
It is still another object of the invention to provide a multiple layered bag which permits sizing modifications by a packager prior to filling and final closure, while still providing protection against moisture and fine particle migration.
Yet another object of the invention is to provide such a bag with moisture and fine particle migration protection, which yet permits the opening and reclosure of an inner sealable bag.
Yet a further object of the invention is to provide a bag, for use in protecting and transporting materials and preventing the infiltration of moisture and fine particle migration, which bag is openable and reclosable, and can be used on automated manufacturing machinery.
These and other objects of the invention will become apparent in light of the present Specification, Claims and Drawings.